// Package clublog uses the ClubLog Country File (cty.xml) to resolve callsign
// EXCEPTIONS — date-ranged full-callsign overrides for DXpeditions and special
// operations that prefix-based files (cty.dat) get wrong. e.g. VK2/SP9FIH was
// Lord Howe Island (not Australia) between specific 2025 dates.
package clublog

import (
	"compress/gzip"
	"encoding/xml"
	"fmt"
	"io"
	"strings"
	"time"
)

// Exception is one date-ranged full-callsign override.
type Exception struct {
	Call   string
	Entity string
	ADIF   int
	CQZ    int
	Cont   string
	Lat    float64
	Lon    float64
	Start  time.Time // zero = no lower bound
	End    time.Time // zero = no upper bound
}

func (e Exception) covers(t time.Time) bool {
	if !e.Start.IsZero() && t.Before(e.Start) {
		return false
	}
	if !e.End.IsZero() && t.After(e.End) {
		return false
	}
	return true
}

// DB holds the parsed exception list, keyed by upper-cased callsign.
type DB struct {
	exceptions map[string][]Exception
	date       string // cty.xml generation date (for the UI)
	count      int
}

// Count returns how many exceptions were loaded.
func (db *DB) Count() int { return db.count }

// Date returns the cty.xml generation timestamp.
func (db *DB) Date() string { return db.date }

// xml decode shapes.
type xlException struct {
	Call   string `xml:"call"`
	Entity string `xml:"entity"`
	ADIF   int    `xml:"adif"`
	CQZ    int    `xml:"cqz"`
	Cont   string `xml:"cont"`
	Long   string `xml:"long"`
	Lat    string `xml:"lat"`
	Start  string `xml:"start"`
	End    string `xml:"end"`
}

// LoadGzip parses a gzipped ClubLog cty.xml stream.
func LoadGzip(r io.Reader) (*DB, error) {
	zr, err := gzip.NewReader(r)
	if err != nil {
		return nil, fmt.Errorf("gunzip: %w", err)
	}
	defer zr.Close()
	return Load(zr)
}

// Load parses a (plain) ClubLog cty.xml stream, extracting only the
// <exceptions> section via a streaming decoder (the file is ~10 MB).
func Load(r io.Reader) (*DB, error) {
	db := &DB{exceptions: map[string][]Exception{}}
	dec := xml.NewDecoder(r)
	for {
		tok, err := dec.Token()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("xml: %w", err)
		}
		se, ok := tok.(xml.StartElement)
		if !ok {
			continue
		}
		switch se.Name.Local {
		case "clublog":
			for _, a := range se.Attr {
				if a.Name.Local == "date" {
					db.date = a.Value
				}
			}
		case "exception":
			var x xlException
			if err := dec.DecodeElement(&x, &se); err != nil {
				continue
			}
			call := strings.ToUpper(strings.TrimSpace(x.Call))
			if call == "" || x.ADIF == 0 {
				continue
			}
			e := Exception{
				Call: call, Entity: x.Entity, ADIF: x.ADIF, CQZ: x.CQZ,
				Cont: strings.ToUpper(strings.TrimSpace(x.Cont)),
				Lat:  parseFloat(x.Lat), Lon: parseFloat(x.Long),
				Start: parseTime(x.Start), End: parseTime(x.End),
			}
			db.exceptions[call] = append(db.exceptions[call], e)
			db.count++
		}
	}
	return db, nil
}

// Resolve returns the exception for a callsign valid at the given date, if any.
// It tries the call as-is, then with a trailing "/x" affix stripped (so
// VK2/SP9FIH/P still matches the VK2/SP9FIH exception).
func (db *DB) Resolve(call string, date time.Time) (Exception, bool) {
	if db == nil {
		return Exception{}, false
	}
	c := strings.ToUpper(strings.TrimSpace(call))
	for _, key := range candidates(c) {
		for _, e := range db.exceptions[key] {
			if e.covers(date) {
				return e, true
			}
		}
	}
	return Exception{}, false
}

// candidates yields the call and a version with one trailing affix removed.
func candidates(c string) []string {
	out := []string{c}
	if i := strings.LastIndex(c, "/"); i > 0 {
		suffix := c[i+1:]
		// Only strip short operational affixes, not a real prefix override
		// (e.g. keep "VK2/SP9FIH" intact; strip "VK2/SP9FIH/P").
		switch suffix {
		case "P", "M", "MM", "AM", "QRP", "A":
			out = append(out, c[:i])
		}
	}
	return out
}

func parseTime(s string) time.Time {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}
	}
	if t, err := time.Parse(time.RFC3339, s); err == nil {
		return t
	}
	return time.Time{}
}

func parseFloat(s string) float64 {
	s = strings.TrimSpace(s)
	if s == "" {
		return 0
	}
	var f float64
	fmt.Sscanf(s, "%g", &f)
	return f
}